If you intend to install Ubuntu on a computer that supports RST functionality your need first to deactivate this functionality in your computer Bios.
Disclaimer: you may already have Windows installed on the computer that uses RST. If you disable RST in the BIOS or change the RST configuration, Windows may become unbootable, as it may no longer be able to find and use the hard disks.
The Ubuntu installer correctly detects the hard disks and can use them. In this case, you can proceed normally.
The Ubuntu installer detects a conflict with RST and will notify the user that RST configuration is required.
Turning RST off completely in BIOS.
Changing the storage controller protocol from RST to Advanced Host Controller Interface (AHCI).
The change from RST to AHCI may result in the loss of some of the advanced functionality that the RST module offers
Caution: Please note that changes to storage configuration can be destructible and lead to irrecoverable loss of data. If you break a RAID setup, your data may no longer be accessible. Likewise, if you change the controller type from RST to AHCI, Windows may no longer be able to boot.
How to safely configure your windows to Advanced Host Controller Interface (AHCI)
Back your data up first,
Start Registry Editor, and navigate to:
Full tutorial you can find on Ubunto helpdesk